There remains a general trend in integrated circuit (IC) designs for the size of the IC to be scaled down. In particular, in the field of input/output (IO) buffers and/or drivers and integrated circuits therefore, there has been a trend to use ever-smaller transistors.
However, in some applications, such as, but not limited to, the automotive market, it is known that ICs still often require high voltage interfaces, thereby dictating the use of larger transistors. Furthermore, the use of ever-smaller transistors leads to higher transistor stresses, and in particular an increase in bias temperature instability (BTI) stress. Over time, this increase in BTI results in transistor performance degradation.
The maximum BTI stress effect occurs when the transistors are in active use, for example when an inverter is arranged to constantly drive a logic “1” level, thus being under continuous stress. Thus, a typical approach to reduce BTI stress is to introduce transistor toggling or switching, even at a very low toggling frequency, due to the ‘recovery effect’ at the moment the stress is removed. The amount the IC device recovers depends on the length of time the stress occurs: inasmuch as the longer the stress, the less the recovery. U.S. Pat. No. 7,009,905 B2 proposes a mechanism to reduce BTI effects using different modes of a memory operating to change stressed transistors.
FIG. 1 illustrates a known circuit diagram 100 of an IO buffer/driver that utilises toggling/switching transistors 130, 135. Two inputs 105, 110 are input to a buffer part comprising respective NAND logic gate 115 and NOR logic gate 125. The NOR logic gate 125 receives one input 105 that is inverted 120. The IO buffer/driver 100 utilises a primary driver part that comprises toggling/switching transistors 130, 135 to provide an output to a capacitive (or active) load 145. The primary driver part comprises a first transistor 130 that receives an inverted output from the NAND logic gate 115 and a second transistor 135 that receives an output from the NOR logic gate 125. The primary driver transistors 130, 135 may be toggled/switched with a change in the IO driver state, for example by control of one of the input signals, e.g. input 110, thereby reducing their active use time.
However, no interface protocols are known that allow voluntary toggling on IO pads, since this often leads to faults in communication. Notwithstanding this, it is known that some interface protocols allow toggling on the specific signals during “IDLE” mode, whilst maintaining some of the signals passing there through at their defined value.